Electrical motors, such as actuator motors used in automotive applications, include a rotor and a stator. Such electric motors typically include a metal pole housing configured to receive magnets (stator) and a movable armature (rotor). Plastic pole housings with metal sleeve inserts may also be used. Pole housings are used to maintain a magnetic circuit of the electric motor in a closed field or loop manner. The motor operates by having the armature turn inside the pole housing when a voltage is supplied to the motor. Metal pole housings are produced using a variety of different manufacturing processes. For example, the pole housings may be formed by a deep drawn stamping process, a rolling process, an extrusion process, or other suitable forming process.
When an electric motor is energized, the armature rotates because wires on the armature are arranged relative to the magnetic field so that torque is developed about an axis of rotation of the armature. The armature includes a shaft having a first portion which extends into a nose of the pole housing. The armature shaft also includes a second portion which extends into a gear box. In order to support the rotating armature, first and second bushings are typically used on the first and second portions, respectively, of the armature shaft.
In certain applications, such as a window lift motor application, for example, cylindrical or sleeve bushings are used in the nose of the pole housing and spherical bearings are used in the brush card to support the armature shaft. Typically, these bushings are made from a sintered iron-based material. These sintered bushings are usually impregnated with grease or oil to provide low friction contact with the armature shaft during rotation of the armature.
The first bushing is press fit into a nose of the pole housing to support radial loads from the armature under static or dynamic conditions. In order to support an axial load on the armature in conventional motors, a reinforced plastic end plug or thrust button is typically coupled to an end of the armature shaft. This thrust button is used to reduce the thumping or rubbing noises during motor operation by avoiding asperity (metal-to-metal) contact between the metal armature shaft and metal pole housing in an axial direction. Therefore, the cost of electric motors is increased due to the need to provide multiple separate components for supporting the armature (rotor) in the pole housing and the associated inventory and assembly costs for these multiple components. These multiple components include sintered bushings, a thrust button coupled to an end of the armature shaft, a broached end of the armature shaft to receive the thrust button, grease or oil for the bushings, and retainers for the bushings.
The present invention reduces the required components substantially by using a polymeric bearing having an integral, flexible end portion to provide multi-axis dynamic load support for the armature shaft within the pole housing. The improved bearing of the present invention is a cup-shaped bearing having a cylindrical body portion with a rigid wall for supporting a side wall of an armature shaft of the electric motor. The rigid wall of the body portion of the bearing supports radial dynamic loads on the armature shaft. The improved bearing also includes a flexible end or base formed integrally with cylindrical body portion. The base supports axial dynamic loads on the armature shaft. The flexible base has a predetermined spring constant to maintain a preload condition on the armature shaft, thereby reducing movement of the armature shaft during operation of the motor.
In an illustrated embodiment, at least an inner surface of the bearing which contacts the armature shaft is coated with a PTFE polymeric material having a low coefficient of friction and high self-lubricating characteristics. The improved bearing of the present invention eliminates the need to use sintered bearings, separate thrust buttons coupled to the end of the armature shaft to absorb axial loads, a broached end of the armature shaft to receive the thrust button, grease or oil on the bearings, or retainer clips for the bearings.
In one illustrated embodiment of the present invention, a bearing is provided for an electric motor. The bearing comprises a body portion having an open end configured to receive a portion of an armature shaft of an electric motor therein, a base configured to apply a spring force to an end of the armature shaft, and a connecting portion located between the body portion and the base. The connecting portion is configured to provide a predetermined spring constant for the spring force applied by the base.
In one illustrated embodiment, the body portion, the base and the connecting portion are integrally formed as a one-piece bearing. Also in an illustrated embodiment, the body portion further comprises means for retaining the body portion in a housing of the electric motor.
In another illustrated embodiment of the present invention, a bearing for an electric motor comprises a body portion having an open end configured to receive a portion of an armature shaft of an electric motor therein. The body portion is configured to support radial loads on the armature shaft in a direction normal to a longitudinal axis of the armature shaft. The bearing also comprises means formed integrally with the body portion for applying a force to the armature shaft in an axial direction generally parallel to the longitudinal axis of the armature shaft.
In yet another illustrated embodiment of the present invention, a bearing for an electric motor comprises a generally cylindrical body portion configured to receive and surround a portion of an armature shaft of an electric motor. The body portion has an inner surface and an outer surface. The inner surface is configured to engage the armature shaft to support radial loads on the armature shaft in a direction normal to a longitudinal axis of the armature shaft. The bearing also comprises means formed integrally with the body portion for retaining the body portion in a housing of the electric motor. The retaining means extends radially outwardly beyond the outer surface of the body portion.
In a further illustrated embodiment of the present invention, an electric motor comprises a housing including a body portion having a nose and an open end opposite from the nose. The open end of the housing provides access to an interior region of the housing. The motor also comprises a magnet structure located in the interior region of the housing, and an armature located in the interior region of the housing. The armature includes an armature shaft having a portion located in the nose of the housing. The armature and armature shaft are rotatable relative to the magnet structure. The electric motor further comprises a bearing located in the nose of the housing. The bearing includes a body portion having an open end configured to receive a portion of the armature shaft and a base formed integrally with the body portion. The base is configured to apply a spring force to an end of the armature shaft in an axial direction generally parallel to the longitudinal axis of the armature shaft.
Additional features of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the invention as presently perceived.